It sounds like something from a science fiction film, a doomsday vault, dug into a frozen mountainside deep in an Arctic island's permafrost that will serve as a Noah's Ark for world seeds in case of a global catastrophe.

But Norway's ambitious project is on its way to becoming reality with start of construction Monday of the Svalbard Global Seed Vault, designed to house as many as 3 million of the world's crop seeds.

Prime ministers of Norway, Sweden, Denmark, Finland and Iceland attended a cornerstone ceremony Monday near the town of Longyearbyen, in Norway's remote Svalbard Islands, roughly 620 miles from the North Pole.

"This seed bank is of global importance. It will be the only one of its kind," Norwegian Prime Minister Jens Stoltenberg said. "It is our final safety net."

Norway's Agriculture Minister Terje Riis-Johansen has called the vault a "Noah's Ark on Svalbard" for its aim to offer the world a chance to restart growth of food crops that may have been wiped out by plant epidemics, nuclear war, natural disasters or climate change.

The foil-packaged seeds will be stored at such temperatures that they could last thousands of years, according to the independent Global Crop Diversity Trust. The trust, founded in 2004, has also worked on the project and will help run the vault, which is planned to open and start accepting seeds from around the world in September 2007.

At the ceremony, Nordic prime ministers poured seeds into a hollowed-out cornerstone which they then placed on the site. Stoltenberg quoted an old Norwegian expression: "From small seeds, big trees grow."

Oil-rich Norway first proposed the idea a year ago, drawing wide international interest. The Svalbard Archipelago, 300 miles north of the mainland, was selected because it is remote and far from many threats, as well as for its cold climate and permafrost.

The Nordic nation is footing the bill of up to about $4.8 million for infrastructure costs.

Cary Fowler, executive secretary of the Global Crop Diversity Trust who led a feasibility study on the project, said that crop diversity is also threatened by "accidents, mismanagement and shortsighted budget cuts."

Already, some 1,400 seed banks around the world, most of them national, hold samples of a country's crops.

But these banks "can be affected by shutdowns, natural disasters, war or simply a lack of money," Riis-Johansen, the agriculture minister, said.

Having duplicate seeds in the Svalbard vault is meant to offer a fail-safe system for the planet.

Svalbard's remote location and permafrost will help protect the seeds and safeguard their genetic makeup, experts say. The vault will have thick concrete walls, and even if all cooling systems fail, the temperature in the frozen mountain will never rise above freezing due to permafrost.

While the facility will be fenced in and guarded, Svalbard's free-roaming polar bears, known for their ferocity, could also act as natural guardians, according to the Trust.

The idea of a global seed bank has been around since the early 1980s but unresolved issues, such as ownership rights to genetic material, stalled it until the U.N. Food and Agriculture Organization adopted the International Treaty on Plant Genetic Resources for Food and Agriculture in 2001.

While Norway will own the vault itself, countries sending seeds will own the material they deposit, much as with a bank safe deposit box. The Global Crop Diversity Trust will help developing countries pay the cost of preparing and sending seeds.